crypto/tls: add initial client implementation.

src/pkg/crypto/tls/ca_set.go

+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tls
+
+import (
+        "crypto/x509";
+        "encoding/pem";
+)
+
+// A CASet is a set of certificates.
+type CASet struct {
+        bySubjectKeyId  map[string]*x509.Certificate;
+        byName          map[string]*x509.Certificate;
+}
+
+func NewCASet() *CASet {
+        return &CASet{
+                make(map[string]*x509.Certificate),
+                make(map[string]*x509.Certificate),
+        }
+}
+
+func nameToKey(name *x509.Name) string {
+        return name.Country + "/" + name.OrganizationalUnit + "/" + name.OrganizationalUnit + "/" + name.CommonName
+}
+
+// FindParent attempts to find the certificate in s which signs the given
+// certificate. If no such certificate can be found, it returns nil.
+func (s *CASet) FindParent(cert *x509.Certificate) (parent *x509.Certificate) {
+        var ok bool;
+
+        if len(cert.AuthorityKeyId) > 0 {
+                parent, ok = s.bySubjectKeyId[string(cert.AuthorityKeyId)]
+        } else {
+                parent, ok = s.byName[nameToKey(&cert.Issuer)]
+        }
+
+        if !ok {
+                return nil
+        }
+        return parent;
+}
+
+// SetFromPEM attempts to parse a series of PEM encoded root certificates. It
+// appends any certificates found to s and returns true if any certificates
+// were successfully parsed. On many Linux systems, /etc/ssl/cert.pem will
+// contains the system wide set of root CAs in a format suitable for this
+// function.
+func (s *CASet) SetFromPEM(pemCerts []byte) (ok bool) {
+        for len(pemCerts) > 0 {
+                var block *pem.Block;
+                block, pemCerts = pem.Decode(pemCerts);
+                if block == nil {
+                        break
+                }
+                if block.Type != "CERTIFICATE" || len(block.Headers) != 0 {
+                        continue
+                }
+
+                cert, err := x509.ParseCertificate(block.Bytes);
+                if err != nil {
+                        continue
+                }
+
+                if len(cert.SubjectKeyId) > 0 {
+                        s.bySubjectKeyId[string(cert.SubjectKeyId)] = cert
+                }
+                s.byName[nameToKey(&cert.Subject)] = cert;
+                ok = true;
+        }
+
+        return;
+}